In a small workshop on the eighth floor of Huaqiang Electronics World’s Building Number Two, Billy Frese is tinkering with his latest invention. The University of California, Berkeley bioengineering graduate explains how the Lief, a vibrating electrocardiogram patch that sits on the skin next to the heart, will help wearers to manage stress and anxiety by measuring the organ’s electrical activity and responding with vibrations to guide the wearer’s breathing. “It’s kind of meditation on training wheels,” he says.

Frese, who is the chief technology officer and part owner of Lief Therapeutics, has just returned from a trip to inspect conditions at a nearby battery factory. “I showed it to them, I said ‘it goes over your heart’,” he motions, “so our batteries need to be safe.”

Around 9% of Lief Therapeutics has been bought by the Shenzhen-based hardware accelerator HAX, which is in turn owned by the venture capital firm SOSV, based in Princeton, New Jersey.

In HAX’s open-plan office, rows of mostly young, foreign teams are developing their own inventions, sandwiched between containers of protein powder and upside-down rucksacks. Benjamin Joffe — one of HAX’s general partners — motions to an industrial robot arm about the size of a desk lamp, which he says is about to be bought by a major car manufacturer.

HAX is in Shenzhen, says Joffe, because of the city’s tech “ecosystem”. “You need to have circuit manufacturers, you need to have the component supplier, the metal parts, the plastic parts, the coating, the certification testing, all those things in reasonable proximity.” HAX’s actual workshop is small because Shenzhen offers so many outsourcing options, he explains. And the extra capacity in the supply chain is a boon for inventors, with factories more willing to deliver on small-scale orders.

That same ecosystem breeds competition. Of around 1,000 hardware start-ups that apply to join the HAX programme each year, only 30 are successful.